﻿	<p>The <em>IfcSharedBldgServiceElements</em> schema in the interoperability 
    layer defines basic concepts required for interoperability primarily between 
    Building Service domain extensions, notably <em>IfcHvacDomain</em>, 
    <em>IfcPlumbingFireProtectionDomain</em>, <em>IfcElectricalDomain</em> and 
    <em>IfcBuildingControlsDomain</em>. This schema includes concepts such as 
    basic type and occurrence definitions for flow and distribution systems 
    and property sets for common building service scenarios such as fluid-flow properties, electrical properties, and space thermal properties.</p>

<p>Figure 270 illustrates the concepts of type, occurrence and performance. Types are specializations of <em>IfcDistributionElementType</em> while occurrences are specializations of <em>IfcDistributionElement</em>. A third theme, defined in the <em>IfcControlExtension</em> schema, relates to the performance characteristics of an occurrence using instances of the <em>IfcPerformanceHistory</em> entity.</p>
<p>A type can have zero or many occurrences. Each occurrence can have many performance history entities associated with it, allowing data that is specific to a certain phase of the lifecycle to be captured and maintained throughout the life of the dataset.</p>

<table>
<tr> <td valign="top" align="center"><img src="../../figures/ifcdistributionport_conceptslide2.gif" alt="type, occurrence and performance history concepts" border="0"></td></tr>
<tr><td><p class="figure">Figure 270 &mdash; Building service lifecycle</p></td> </tr>  
</table>

<p>The <em>IfcSharedBldgServiceElements</em> schema specializes building services concepts symmetrically for occurrences and types, with the <em>primary</em> functional role of the entity determining its classification into the following generic concepts: 
<ul>
<li><b>Distribution Chamber</b>: a formed volume used in a distribution system, such as a sump, trench or manhole.</li>
<li><b>Energy Conversion Device</b>: a building systems device that converts energy from one form into another such as a boiler (combusting gas to heat water), chiller (using a refrigeration cycle to cool a liquid), or a cooling coil (using the phase-change characteristics of a refrigerant to cool air).</li>
<li><b>Flow Controller</b>: a device that regulates flow within a distribution system, such as a valve in a piping system, modulating damper in an air distribution system, or electrical switch in an electrical distribution system.</li>
<li><b>Flow Fitting</b>: a device that is used to interconnect flow segments or other fittings within a distribution system, such as a tee in a ducted system that branches flow into two directions, or a junction box in an electrical distribution system.</li>
<li><b>Flow Moving Device</b>: a device that is used to produce a pressure differential in a distribution system, such as a pump, fan, or compressor.</li>
<li><b>Flow Segment</b>: a section of a distribution system, such as a duct, pipe, or conduit.</li>
<li><b>Flow Storage Device</b>: a device used for the temporary storage of a substance (solid, liquid, or gas) such as a tank, or the voltage potential induced by the induced electron flow (a battery).</li>
<li><b>Flow Terminal</b>: acts as a terminus or beginning element in a distribution system such as a ceiling register in a ducted air distribution system, a sink in a waste-water system, or a light fixture in an electrical lighting system.</li>
<li><b>Flow Treatment Device</b>: a device used to change the physical properties of the medium, such as an air, oil or water filter (used to remove particulates from the fluid), or a duct silencer (used to attenuate noise).</li>
</ul>
</p>

<p>Refer to the domain schemas where types and occurrences are further elaborated using <em>PredefinedType</em> enumerations for examples of the range of supported concepts within these broad classifications. If a new type is needed within this classification, extend using the ElementType attribute. However, if a completely new concept is required that does not fit within this classification, use instances of the generic <em>IfcDistributionElementType</em> and <em>IfcDistributionElement</em> entities for the type/occurrence objects as needed. </p>

<p>Occurrences in a distribution system are typically coupled together using instances of <em>IfcDistributionPort</em>. This is also where concepts such as mass-flow properties are applied based on performance characteristics. Refer to the <em>IfcDistributionPort</em> documentation within this schema for further elaboration on coupling together components in a distribution system and tracking the flow characteristics across the port boundaries. </p>

<blockquote class="history">HISTORY  This schema has been significantly modified in IFC2x2. Refer to the change log and issues resolution database for details.</blockquote>
